EMPIRICAL STRENGTH ENVELOPE FOR SHALE

2016 ◽  
Vol 78 (7-3) ◽  
Author(s):  
Mohd For Mohd Amin ◽  
Nur‘Ain Mat Yusof ◽  
Rini Asnida Abdullah
Keyword(s):  
Failure Criterion ◽  
Sedimentary Rock ◽  
Triaxial Compression ◽  
Compression Tests ◽  
Failure Envelope ◽  
Rock Samples ◽  
Failure Envelopes ◽  
Project Site ◽  
Coulomb Criterion ◽  
Triaxial Compression Tests

Effectively, strength envelope describes behavior of rock when subjected to common stresses in construction, i.e. compressive, triaxial and tensile stresses. This study is aimed at investigating the strength envelope for shale, a sedimentary rock obtained from dam project site in Baram, Sarawak. Series of triaxial compression tests were carried out to obtain the strength envelope for the rock samples. For verification of failure criterion, uniaxial compression and Brazilian tests were also conducted on the rock samples. Results from the relevant tests were analysed using RocData software to obtain the strength envelope. Subsequently, Mohr-Coulomb and Hoek-Brown failure criterion are used to determine failure envelop for the rock samples. Based on the failure envelopes and the related strengths (i.e. compressive and tensile strength), suitability of both approach, in defining strength envelope for shale, is verified. The study shows that for highly laminated sedimentary rock like shale, Hoek-Brown criterion gave a more representative failure behaviour. The failure envelope clearly shown all the strength limits when the rock is subjected to triaxial, uniaxial and tensile stress, which is not clearly shown in the Mohr-Coulomb criterion. Therefore, Hoek-Brown criterion is a more appropriate method for describing strength envelope, as it able to show the limiting stresses when rock samples are subjected to common stresses in construction.

Strength envelope of granular soil stabilized by multi-axial geogrid in large triaxial tests

2020 ◽  
Vol 57 (3) ◽  
pp. 448-452 ◽  
Author(s):  
A.S. Lees ◽  
J. Clausen
Keyword(s):  
Triaxial Compression ◽  
Triaxial Tests ◽  
Compression Tests ◽  
Failure Envelope ◽  
Element Analysis ◽  
Linear Elastic ◽  
Perfectly Plastic ◽  
Elastic Perfectly Plastic ◽  
Triaxial Compression Tests ◽  
Properties Of Soil

Conventional methods of characterizing the mechanical properties of soil and geogrid separately are not suited to multi-axial stabilizing geogrid that depends critically on the interaction between soil particles and geogrid. This has been overcome by testing the soil and geogrid product together as one composite material in large specimen triaxial compression tests and fitting a nonlinear failure envelope to the peak failure states. As such, the performance of stabilizing, multi-axial geogrid can be characterized in a measurable way. The failure envelope was adopted in a linear elastic – perfectly plastic constitutive model and implemented into finite element analysis, incorporating a linear variation of enhanced strength with distance from the geogrid plane. This was shown to produce reasonably accurate simulations of triaxial compression tests of both stabilized and nonstabilized specimens at all the confining stresses tested with one set of input parameters for the failure envelope and its variation with distance from the geogrid plane.

The Application of Coreless Inductors for Displacement Measurements in Laboratory Investigations of Rock Properties

2014 ◽  
Vol 59 (4) ◽  
pp. 1033-1050
Author(s):  
Janusz Nurkowski
Keyword(s):  
Temperature Compensation ◽  
Measurement Accuracy ◽  
Triaxial Compression ◽  
Rock Properties ◽  
Variable Pressure ◽  
Compression Tests ◽  
Rock Samples ◽  
Laboratory Investigations ◽  
The Impact ◽  
Triaxial Compression Tests

Abstract The paper presented the coreless inductive sensor, its construction and principle of operation. The impact of temperature on the outcome of a measurement performed with the inductor was discusses, together with the possibility of temperature compensation of the inductor’s performance. Subsequently, the reasons for limited measurement accuracy and resolution were discussed, particularly under the variable pressure in the order of some hundreds MPa. Two types of such sensor were presented: a sensor for measuring linear strains, e.g. during compressibility measurements, and an sensor for measuring circumferential strains during triaxial compression tests. Additionally, the manners of fixing the sensor on rock samples were presented. Finally, some examples of the sensor application were shown, together with the results of measurements of deformations of rock samples - especially in cases when resistance gauges cannot be used, and the samples are subjected to a load in the uniaxial and triaxial system, under the hydrostatic pressure of up to 400 MPa and the normal one.

scholarly journals Stress Drop as a Result of Splitting, Brittle and Transitional Faulting of Rock Samples in Uniaxial and Triaxial Compression Tests

2015 ◽  
Vol 37 (1) ◽  
pp. 17-23 ◽  
Author(s):  
Jerzy Cieślik
Keyword(s):  
Stress Drop ◽  
Rock Sample ◽  
Triaxial Compression ◽  
Failure Process ◽  
Strength Loss ◽  
Axial Stiffness ◽  
Compression Tests ◽  
Rock Samples ◽  
Test Pressure ◽  
Triaxial Compression Tests

Abstract Rock samples can behave brittle, transitional or ductile depending on test pressure, rate of loading and temperature. Axial stiffness and its changes, relative and absolute dilatancy, yield, and fracture thresholds, residual strength are strongly pressure dependent. In this paper the stress drop as an effect of rock sample strength loss due to failure was analyzed. Uniaxial and triaxial experiments on three types of rock were performed to investigate the stress drop phenomenon. The paper first introduces short background on rock behavior and parameters defining a failure process under uniaxial and triaxial loading conditions. Stress drop data collected with experiments are analyzed and its pressure dependence phenomenon is described. Two methods for evaluation of stress drop value are presented.

scholarly journals Evolution of Strength Parameters for Sandstone Specimens during Triaxial Compression Tests

2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Xiang Ding ◽  
Na Chen ◽  
Fan Zhang ◽  
Guangqing Zhang
Keyword(s):  
Stress Tensor ◽  
Triaxial Compression ◽  
Cohesive Strength ◽  
Compression Tests ◽  
Strength Parameters ◽  
Frictional Strength ◽  
Coulomb Criterion ◽  
First Time ◽  
Triaxial Compression Tests ◽  
Deviatoric Stress Tensor

Despite the lack of test data of the coefficient of pressure sensitivity α and the shearing cohesion k, the Drucker–Prager criterion is commonly applied for numerical analyses of geotechnical engineering. To bridge the gap between the wide application and insufficient knowledge of strength parameters of the Drucker–Prager criterion, this study presents experimentally calibrated strength parameters of this criterion for the first time. This paper proposes a new method to measure α and k in the Drucker–Prager criterion. The square root of the second invariant of the deviatoric stress tensor J 2 is linearly fitted with the first invariant of the stress tensor I 1 in the stress space. The parameters φ and c in the Mohr–Coulomb criterion and α and k in the Drucker–Prager criterion are calibrated to the same set of triaxial compression tests of sandstones. With these testing results, five pairs of conversion formulae (which are most commonly used in the literature) are examined and the most appropriate pair of conversion formulae is identified. With parameters indicating cohesive strength (c and k) and parameters indicating frictional strength ( φ and α ), the evolutions of different strength components are compared with those in the cohesion-weakening friction-strengthening model. With an increase in plastic deformation, the cohesive strength parameters c and k firstly increase to a peak value and then decrease. The frictional strength parameters φ and α gradually increase at a decreasing rate after the initial yield point.

Inverse analysis–based interpretation of sand behavior from triaxial compression tests subjected to full end restraint

2009 ◽  
Vol 46 (7) ◽  
pp. 768-791 ◽  
Author(s):  
Youssef M.A. Hashash ◽  
Qingwei Fu ◽  
Jamshid Ghaboussi ◽  
Poul V. Lade ◽  
Christopher Saucier
Keyword(s):  
Principal Stress ◽  
Failure Criterion ◽  
Laboratory Testing ◽  
Inverse Analysis ◽  
Triaxial Compression ◽  
Boundary Value ◽  
Octahedral Plane ◽  
Compression Tests ◽  
Soil Behavior ◽  
Triaxial Compression Tests

Current laboratory testing often imposes or assumes uniform stress and strain distribution in a specimen for convenient data reduction to interpret soil behavior. This paper presents an inverse analysis framework, Self-learning Simulations (SelfSim), to interpret the drained behavior of sand from triaxial compression tests with fully frictional loading platens. The frictional platens result in significant bulging of and nonuniform stresses and strains within sand specimens. SelfSim treats the specimen as a boundary value problem (BVP) and extracts these nonuniform stresses and strains from within each specimen using external load and displacement measurements. The extracted behavior shows significant principal stress rotation, variation of intermediate principal stress, and nonuniform volume change throughout the specimen. Mobilized friction angles are interpreted on the two-dimensional slip surface associated with the Mohr–Coulomb failure criterion, on the octahedral plane associated with the Drucker–Prager failure criterion, and on the spatially mobilized plane (SMP) associated with the Matsuoka–Nakai failure criterion. The extracted stress–strain behavior is used to examine the sand’s stress-dilatancy characteristics. Proposed integration of SelfSim inverse analysis with laboratory testing opens the way for new and efficient approaches to soil behavior characterization under general loading conditions, needed for the solution of general geotechnical boundary value problems, from readily available laboratory tests.

A Simple Unconsolidated Undrained Triaxial Compression Test Emulator

2015 ◽  
Vol 771 ◽  
pp. 104-107
Author(s):  
Riska Ekawita ◽  
Hasbullah Nawir ◽  
Suprijadi ◽  
Khairurrijal
Keyword(s):  
Triaxial Compression ◽  
Measurement Data ◽  
Radial Strain ◽  
Compression Tests ◽  
Viscous Effects ◽  
Axial Pressure ◽  
Strain Stress ◽  
The University ◽  
And Storage ◽  
Triaxial Compression Tests

An unconsolidated undrained (UU) test is one type of triaxial compression tests based on the nature of loading and drainage conditions. In order to imitate the UU triaxial compression tests, a UU triaxial emulator with a graphical user interface (GUI) was developed. It has 5 deformation sensors (4 radial deformations and one vertical deformation) and one axial pressure sensor. In addition, other inputs of the emulator are the cell pressure, the height of sample, and the diameter of sample, which are provided by the user. The emulator also facilitates the analysis and storage of measurement data. Deformation data fed to the emulator were obtained from real measurements [H. Nawir, Viscous effects on yielding characteristics of sand in triaxial compression, Dissertation, Civil Eng. Dept., The University of Tokyo, 2002]. Using the measurement data, the stress vs radial strain, stress vs vertical strain, and Mohr-Coulomb circle curves were obtained and displayed by the emulator.

scholarly journals Semi-empirical elastic–thermoviscoplastic model for clay

2016 ◽  
Vol 53 (10) ◽  
pp. 1583-1599 ◽  
Author(s):  
David Kurz ◽  
Jitendra Sharma ◽  
Marolo Alfaro ◽  
Jim Graham
Keyword(s):  
Stress Level ◽  
Axial Strain ◽  
Triaxial Compression ◽  
Compression Tests ◽  
One Dimensional ◽  
Load Duration ◽  
Compression Creep ◽  
Overconsolidated Clays ◽  
Semi Empirical ◽  
Triaxial Compression Tests

Clays exhibit creep in compression and shear. In one-dimensional compression, creep is commonly known as “secondary compression” even though it is also a significant component of deformations resulting from shear straining. It reflects viscous behaviour in clays and therefore depends on load duration, stress level, the ratio of shear stress to compression stress, strain rate, and temperature. Research described in the paper partitions strains into elastic (recoverable) and plastic (nonrecoverable) components. The plastic component includes viscous strains defined by a creep rate coefficient ψ that varies with plasticity index and temperature (T), but not with stress level or overconsolidation ratio (OCR). Earlier elastic–viscoplastic (EVP) models have been modified so that ψ = ψ(T) in a new elastic–thermoviscoplastic (ETVP) model. The paper provides a sensitivity analysis of simulated results from undrained (CIŪ) triaxial compression tests for normally consolidated and lightly overconsolidated clays. Axial strain rates range from 0.15%/day to 15%/day, and temperatures from 28 to 100 °C.

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